When a magnet is vibrated so that the magnet passes through the inside of a conductive coil, an induced current flows in the coil to generate an electromotive force. The electromotive force is generally small on the order of milliwatts. A conceivable method for enhancing the electromotive force is to use a plurality of magnets and a plurality of coils.
As a related art, there is given one generator including a plurality of coils arranged around magnets in which the same poles are opposed to each other, and the magnets and the coils are desired to have equal lengths and be arranged at equal intervals (see, for example, Patent Literature 1). Then, when a gap between the magnets is halved, a larger electromotive force may be obtained.
As another related art, there is also given a vibration power generator configured to use a plurality of permanent magnets and a plurality of coils surrounding the permanent magnets to generate an electric power through relative movement with vibration. In the vibration power generator, the permanent magnets are arranged so that the same poles are opposed to each other, and integrated together to have a gap therebetween, and the plurality of coils are arranged on the outer peripheries of the plurality of permanent magnets so as to have a distance from the permanent magnets. The plurality of coils wound in opposite directions are alternately arranged, and the length of each coil is set to 70% to 90% of the length of the permanent magnet (see, for example, Patent Literature 2). In Patent Literature 2, FIGS. 4 and 9 show that the electromotive force is enhanced.